Automatic telephone system



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|\\O m 1lb Hw /fh /Um E @E E Hw Y Q* m n n mi. ha v... 'Inu m... C W0-Qn .W QQ\ Nfmanznders I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I lI I I l I I I I I I I f AUTOMATIC TELEPHONE SYSTEM ofiginal Filed Feb. 2, 1942 I `14 Sheets-sheet 14 rE/v Pff/my GROUPS Lc-z GROUPS I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Reissued Dec. 17, 1946 AUTOMATIC TELEPHONE SYSTEM Norman H. Saunders, Chicago, Ill., assignor to Kellogg Switchboard and Supply Company, Chicago, Ill., a corporation of Illinois original No. 2,333,744, dated November s, 1943,

Serial No. 429,232, February 2, 194.2. Application lfor reissue September 9, 1944, Serial No.

This invention relates to automatic telephone systems, and its object is to provide an economical and reliable automatic telephone system arranged to provide the various services which have heretofore been found necessary or desirable in connection with the subscriber lines.

This application is a continuation in part of my prior application Serial No. 400,990, filed July 3, 1941. y

GENERAL DESCRIPTION In addition to providing regular telephone service for individual subscriber lines, it is necessary or at least desirable that automatic telephone systems provide the following services:

1. Party-line service, which includes the selection of the called party line and the signaling of the desired substation thereon;

2. Reverting-call party-line service, in which a subscriber at one substation on a party line is able to call a subscriber at any other substation on the same party line;

3. P. B. X service, the provision of a group of subscriber lines having a common directory number, with arrangements for selecting and making connection with an idle line of the group when the common directory number is called;

4. Non-busy-line servi-ce, the provision of a line which is not made busy when called, enabling a number of contemporaneous calls to be made to such line;

5. Call-holding service, the provision of arrangements for enabling-calls to a desired substation to be held therefrom, as when a subscriber is being annoyed by anonymous calls;

6. Secretarial service, the provision enabling the calls directed to a substation while the subscriber is absentJ to be routed to a secretarys telephone; and

7. Intercepting service, the provision of arrangements enabling calls to a disconnected substation to be routed to an intercepting operator.

It is an object o-f the invention to provide services such as those mentioned above through the provision of equipment common to all of the connecting-link circuits serving a group of lines (100 lines in the illustrated example).

It has been chosen to illustrate the invention a applied to an automatic telephone system of the type employing small-capacity primary and secondary switches in tandem to replace the largecapacity switches heretofore used as line iinders` and connectors. The disclosed tandem arrangement of the small-capacity switches incorporates 46 claims. (ci. 179-17) a number of features of improvement in addition to those previously enumerated.

As will be described more fully hereinafter, the subscriber lines are divided into what are termed large groups (of lines each); subgroups of small-capacity primary and secondary switching devices are provided in each large group to handle .both the originating and terminating calls; and control equipment common to all the primary and secondary switching devices of a large group -is provided to position these devices for extending originating or finder-action connections, which common control equipment also responds to position the required primary and secondary switching devices to complete terminating of connector-action connections, the dialed line-designating digits for each call being stored for this purpose and then transferred, call-by-call, to the common equipment as the common equipment becomes available.

A specific object is the production of a system of the character under consideration wherein control equipment common to all of the primary and secondary switching devices of a large group is provided to control the setting of these devices in outgoing `of iinder-action connections, which common equipment also responds in substantially the same Way to position the required primary and secondary switches for incoming or connector action, the dialed tens and units digits for each call being stored for this purpose and then transferred, call-by-call, to the common equipment as it becomes available.

A feature of the disclosed arrangement is that the digit-storage equipment is associated with the connecting-link circuit (the circuits which control the setting-up oi incoming or connector-action connections). A further feature is that the distributing device associated with each such link circuit has access to each secondary device allotted to extend connector-action calls to the primary devices, whereby no connector-action calls need be lost at any time because of unavailability to the connecting-link circuits of idle connector-action secondary devices.

A further specific object is the production of a system of the character under consideration wherein the equipment vfor providing services such as those enumerated hereinbefore is `provided in connection with the above-mentioned common equipment, whereby the amount of equipment necessary for providing such servi-ces is greatly reduced.

Other objects and features of the invention will appear more fully as the description progresses.

The drawings Referring now to the accompanying drawings, they show by means of the usual circuit diagrams a suiicient amount of the equipment involved in an automatic telephone system embodying. the features of the invention to enable'the invent-ion to be understood.

Figs. 1 to 11 are circuit drawings of the system;

Figs. 12 and 13 illustrate the arrangement of the system; and

Fig. 14 shows the intended arrangement of the sheets of drawings on which Figs. 1 to l1 are drawn.

The system arrangement Referring now particularly to Figs. 12 and 13, the arrangement of the system wll'be described.

The arrangement shown in Fig. 12 illustrates a 1,000-line automatic telephone system comprising ten 10D-line groups, each of which may be arranged as indicated in Fig. 13. Each of the rectangles in Fig. 12 indicates a separate 1D0-line group, each such group having originating-link paths taken for use automatically by primary and secondary nder action within the group when the receiver is removed at a calling substation, each group also having terminating or connectoraction link paths, any idle one of which may be seized when a connection is to be completed toa subscriber line of that group.

The selectors SI, SII, etc. to SSI, located respectively below the 10o-line groups, #1, #2, etc. to #0, are each but one of a number (ten, for example) provided to handle calls originating in the associated 10D-line group. In the illustrated Y1,000-line system, only a single rank of selectors is employed, the illustrated hundreds selecto-rs, If the system illustrated were expanded to a 10,000-line system, two ranks of selectors would be provided, thousands selectors and hundreds selectors; while if it were reduced to a 10C-line system, no selectors at all would be required, each originating or finder-action path being joined to a terminating or connector-action path, as will be understood.

,The illustrated selectors, mechanically, maybe of the usual two-motion type of automatic switch. Where long-life is a factor, the selectors may be of the so-called all-relay type, in which a counting-relay operation occurs responsive to. dialed f impulses to select any one of ten group relays, followed by a hunting-relay action to select an idle link connected up by the group. relay operation. One selector of the latter type suitable for use herein is illustrated in applicants zo-pending application, Serial No. 346,069, filed July 18, 1940, issued April 14, 1942, Patent No. 2,279,531.

Considering, for example, the selector SI of Fig. 12, the rectangle within which the reference character SI is placed may indicate the control relays of the selectors, while each of the sho-rt, heavy lines beneath .this rectangle is intended to indicate a group of contact sets (assumed to be ten in the present example). Each of these groups of contact sets is connected up responsive to the dialing of a separate one of the digits 1 to 9 and 0, as indicated. The fainter lines extending horizontally between illustrated selectors are intended to indicate the multiple between selectors.

The links incoming to the 1D0-line group #1 are reached from 1the first, or digit-1, group of contact sets of all of the selectors; the links incoming to the 1D0-line group #2 .are reached from the second, or digit-2, group of Contact sets of all of the selectors; etc., to the 10D-line group #0, whose incoming links are reached from lthe tenth, or digit-0, group of contact sets of all of the selectors.

v Since the arrangement of any one of the 100- line groups may be similar to those ,of all of the rest of the 10U-line groups, it suices to show the switching and circuit arrangements of a single one of the 1D0-line groups. The 10D-line group #9 has been chosen arbitrarily for this purpose. It is the 1D0-line group whose incoming links are reached throughany'one of the selectors respon- Vsive to the dialing of the digit 9. The switching arrangement of 10D-line group #9 is shown in Fig. 13, while the 'circuit' arrangements lthereof are indicated in Figs. 1 to 11l Referring now particularly to Fig. 13, it will be seen that the selector SBI of Fig. 12 is only one of .ten selectors provided for handling calls originating in 10G-line group #9, the other selectors being S82 to S90, the respective groups of contact sets of all of these selectors being .connected in multiple with each other and with the corresponding groups of contact sets of the selectors reached from the other 10D-line groups.

The one hundred subscriber lines served by 100- line group #9 are subdivided into ten 10-line groups, each served'by a separate group yof primary switching devices. For example, the first lO-line group in Fig. 13 comprises the subscriber lines SII to 9I0, indicated along the top of the drawing and connected in multiple to the selecytive-position contacts of the four primary switching devices IPA, IPB, IPC, and IPD. These switching devices constitute the rst of ten primary groups. The second primary group, including primary switches 2PA to 2PD, serves the second 10-1ine group (lines 92| to 92|!) of the 100- line group #9. The primary vgroups serving the .third to eighth 10-line groups have been omitted for .the sake of compactness, but the primary switching devices (SPA to 9PD and I IJPA to IUPD) which serve the ninth and tenth 10-line groups are indicated.

The lines and line multiple for all ofthe 10-line groups except the rst have been omitted for the sake of simplicity, as each 10-line group is similar to each of the other 10-lir1e groups. It is intended to be'illustrated by the arrangement in Fig. 13 that any idle one of the primary switching devices, such as IPA to IPD, for example, having access to a group of 10 lines can operate to make connection with a calling line, and that any idle one of the said devices can operate to make connection with any called line in Ithe associated l-line group.

The arrangement illustrated in Fig. 13 has been provided on the assumption that four connections (incoming, outgoing, or both) within a 10-line group are suilicient. For the 10U-line group, this provides for a total of forty connections to be made with calling and called lines, which has been shown by experience to be much more .than is required. Accordingly, the total number of connection paths is halved in the secondary groups, as will now be pointed out.

As illustrated in Fig. 13, a total of twenty secondary switching devices (each of 10-line capacity) is provided, and are arranged in four groups, A to D. The secondary devices are ISA to SSA in the A group, ISB to SSB in the B group, ISC ,to SSC'in the C group, and ISD to'ESD in ,the D group. In each secondary group, the selective-position contacts of the switching devices are connected respectively in mul-tiple as indicated, and the ten links thus provided extend respectively to ten primary switching devices, each in a different 10line group. The five secondary devices ISA to 5SA, comprising the A secondary group, have access to the ten A primary devices IPA to IOPA; the B secondary group has access to the ten B primarydevices IPB to IOPB; the C secondary group has access to the ten C primary switching devices IPC to |PC; and the D secondary group has access to the ten D primary switching devices IPD to |0PD. Each of the twenty secondaries, ISA to SD, therefore, has access to each of the line groups of lines, through the illustrated primary Aswitching devices. The common secondary devices are thus more eflicient from a call-handling standpoint than are the primary switching devices in that they receive calls from and extend calls to the large gro-up of one hundred lines, instead of being restricted to a small or 10line group, as is the case of the primaries, The reduction permitted in the number of switching devices or links when the group is enlarged is Well known, and therefor@ need not be further discussed herein.

Of the twenty secondary switching devices, some in each group are allotted to the handling of the originating or iinder-action connections, the remainder being allotted to the handling of terminating or connector-action connections. It is to be observed that devices ISA to 3SA in secondary group A, are assigned to finder action, and are linked respectively to the selectors S8I to S83; the devices ISB to SSB in secondary group B are linked respectively to the selectors S84 to S86; and the rst two devices in each of the C and D secondary groups are linked respectively with the selectors S01 to'S90. The ten remaining secondary switching devices (the last two in each of secondary groups A and B, and the last three in each of the secondary groups C and D), are assigned to connector action, and are therefore linked to the selective-position contacts of the distributing devices, such as DR--I and DR-2.

Since the 10D-line group shown in Fig. 13 is group #9, calls to this group come through the ninth group of contact sets of all of the selectors serving all 1GO-line groups. The link group reached through the ninth selector group of contact sets is shown by a single line extendingV to the left from selector S8I, and then branching out upwardly into ten lines to indicate the ten link paths represented by the ninth selector group. These link paths are all incoming to the 10G-line group #9 of Fig. 13, and they extend respectively to connecting-link circuits CLC-I to CLC-I0, of which only the first two are indicated.

Each connecting-link circuit CLC- l to CLC- I0 has a selective-switching device associated therewith termed herein a distributor. The distributors DRf-I and DR-2 are shown associated respectively with the connecting-link circuits CLC-I and CLC-2. has ten selective-position contact sets, whereby it can associate its individual connecting-link circuit with any one of the ten terminating or connector-action paths leading to the secondar devices assigned to connector action.A

The circuit drawings Referring now to the circuit drawings (Figs. 1 to 11) of the 10D-line group #9, the equipment shown in Figs. 1 and 2 'and in the lowermost portion of Fig. 3 is common equipment con- Cil Each of the distributors trolled from the 10line groups of hundreds group #9. The equipment shown in Fig. 1 includes transfer relay |0I, for changing over from finder action to connector action; test-cutoff relay |02, matching control relays I 03 to |06, controlled according to the instant position of the preference group of relays |01 to ||0 to match an idle one of the four primary switching devices in a calling (or called, as the case may be) 10line group with a secondary group in which there is at least one idle lsecondary device allotted for lnder action (or for connector action, as the case maybe).

Fig. 2 shows ten pairs of tens-connecting relays, each pair being associated with a separate one of the ten 10line groups. Relays 20| and 2|! are associated with the iirst 10line group; 202 and 2I2 are associated with the second'lf line group, etc., to the last pair, relays 2|0 and 220, which are associated with the tenth 10line group.

Relays 2I| to 220 are used both for finder action and for connector action and are arranged to be mutually exclusive in their operation. Each of the relays 2|| to 220 serves, when operated, to connect up the four primary switching devices having` access to the associated 10line group of lines.

The relays 20| to 2 I0 are used for finder action only and each serves, when operated, to connect up the ten marking conductors individual respectively to the ten lines of the associated 10line group, whereby the selected primary device is caused to be set in a position to connect with the instant calling line. For this purpose, each of the relays 20| to 2I0 has ten contact pairs, but for the sake of compactness of the illustration, only the first, second, ninth and tenth contact pairs are illustrated. The relays 22| and 222- are control relays associated with the grou relays 2| I to 220.

The relays 23| to 240 are associated respectively with the ten 10line groups, and each of them serves as a cutoff relay to disconnect the associated 10line group from nder action, when a call is made from a line therein at a time when at least one of the primary switches of the group is idle, but a busy condition in one or more of the secondary groups precludes the completion of the iinder action.y The timer RT associated with the relays 23| to 240 is arranged to unlock any operated one ofv these relays at frequent intervals (every ten seconds, for example) to permit a further test to be made, Relays 223 and 224 are common relays associated with cutoi relays 23| to 240 to bring about the operation thereof as above pointed out.

The units translator shown on the lower part of Fig. 3, comprising the relays 30| to 306, is operated over conductors to 0 of the cable CA-UM through contacts of any one of the relays 20| to 20 to energize the conductors I to E in the cable CA-PM according to the required setting of the relays in any one of the four switching devices of any primary group, such as the switching devices IPA to IPD, Figs. 4 and 3, of the first primaryY group. Relays 30| to 305 serve also to prevent double marking in the event that two lines of the same 10line groupare calling simultaneously.

Although the system arrangement herein disclosed is not limited to any particular yform oi small-capacity switching device, it has been chosen to illustrate the invention as appliedrto a system using all-relay small-capacityV switchcatedfin 3 :as v4a broken-aline rectangle;Y for each cfs these 'devices maybe similantoithe devicesiIPAand IPB.k

Thefswitchingfdevice:IPAQ for example, in: cldesr-fthe lfive*selecting?relays 4H to :4I5, each' ofi-which'has two setsfofi.selective-position 'contacts sthere'onf, The contact sets inY the` upper rovir (three contact pairs to a set) are.'assigned respectively @to f the firstwtol; fifth t lines offtlie associated S10-.line group, i While :the -ri'lye` contact sets-:shownjust belowf the :fones -last 'named are"- assigined'respectively, to the sixth to Jtenth linesi neth'associated= 10-f'1ine group; The 'switching devic'zerv IPA Aincludes 'also a sixth or switching; relayvf; which remains normal when connection is to be made, through the concerned one of the relays'fll H Ito 4 I 5,1With one of vthe i'irst tive lin'es in' fthergroup; but is; operated, along withone. of threlaysuilll' to' 4 f5,'fwhen connection is tofbe made-'with any one of the sixth to tenth lines in the;associated110line=group.` The other smallcapacity switching devices are similar. 's' In addition to the relays 4II to 4I6 whichf'cooperatei'as previously pointed 'out to 'select anl7 deSir'edfe-ne ofthe illustrated tenlcontact sets, the switching device IPA'has associatedtherewith a connection relayM which; among other things, whenioperated,connects up the conductors I to 6 ofthe ucable' CA-PM to permit setting ofthe relays III-"I to 4I 6 'according -to the marking placed n the conductorsfof this cable by the units translator-of-Figlf3 The hold relayi4|fI 'is associated withthe switching device to exercise certain ccntrol -lfunctio'ns'- to 'be hereinafter described.'

Also` shownin' Fig. .3 is a broken-'line rectangle indicative of the primary groups-'2 to 10. It is to lne-observed that Ythe primary marking cable CA-PM extends dotted through this broken-line rectangle'iewhich'is intended to indicate that this cable-multiples into th switching device of eachV4 of Ttheprirnary groups 2`to 10 "as indicated linI connection Withl the primary switching devices IP'A to IPD'bfFgs. 4 and 3.

Of-'the ten'subscrib'er llines served bythe primary switching devices-IPA to" IPD of Figs. 4 and '3,`'only` 'the r'st and sixth lines (#BII and #Bf-6l arel shown: The tip, ring, and sleeve conductors T,`R, and Sfof 'each of these lines are multipled tothe corresponding 4selective-position contacts'fof the associated primari/'devices IPA to kvIPD`v The illustrated rst and sixthlines are served by relay 4H of' "device IPA; the second relay 4I2` serves the second and seventh lines; therthird relay 4I3-serves the third and eighth lines';the fourth relay M4 serves the fourth `and niritli'liries;v and "the-fth'relay l4I5 serves the fth and-tenth linesfof. the associated lil-line group.

Linefttlll. is the `line lvof'. `substation 1A, While line #BI'S "isi the line of` substation B. Line and. cutoff-"relays IIJI- and-402 areindividual to line #fQII' while' line yand cutoff relays :403; and ".404 are" individualtoline` #91 6."

Whereas, the lines#9|l: and `#BIH :are in;` dividual (or single-party) `lines-,flig.; 4A; shows lines #91.1 and #9| B whichfare partylines.; Line #91.1. 'ris..tilllstrated as Ta, vten-party .'line. :having substations #'ilfll'to' #9'I.'I0;thereon, ofr; hich only=substation;#$'|,1I; #9115,f and#9I'|Il .are

The' v-line #9 I 8 .isil 'shownA asH a four-partyvv line, having substationsfalt I8 I: 'toit-9 IBdfrthereonz:

The line'zequipment 'of line'e'i I 8 YcomprisesillnefY andscutaoffrreiays ,46 It :and 462, as Ain therese g offtlie. :individual lines; The .line equipment 'ioffX line '.#9 I 1,-: iniaddition to :line andacutoi Vrelaysifv #Blffandfx452,includes lockout relay 453. This lo'ckouttrelay is', arranged Vto enable y.the exchange i switching Yequipment )to 'be entirely disconnected@ from. tliezfline while a reverting-call" conversation. isr'beingcarrie'd on'overethefline, which con-ver: l sati'bns".4 are "likely" to= be 1 quite frequent because f ofithe :'la'rgenumber (10)" of .substations-foon nected toiline'f#9'| 'I. As willrbe pointed out here"- inafter, :thef/ commonacontrol' equipment 'is `aiti ranged', to distinguish.'betwe'ent'aiipartyline with.

aflockoutrelayand a party line Withouta lockout: relay, and-'to "disconnect-'the switching equipment i from La partysflinesovenwhich .ra reverting call has-been made, on-ly'in the event that suchv partys?.

:line isi equipped? witha. lkout' irelay.

Figli'l 5 :shows"the"secondary switching devicesfiL ISA-'andESB offFig': 13.,"each 'of` which differs: from vone fof thev y'primary switching fdevicesfsuchl" as IPA,'.Fig."4)1'inthat'therefare fourcontact Vpairs toa set (tip, iringfsleeve,y and 1 hold) Flg 'shows'the distribut'o-r"DP '-I "oFFgf 13,." aswell-as thesele'cton-Sl. Th'issele'ctor islas-1 sinned :to be ofthe' `soacalled all-'relay type shown inE applicants Patent `No.2,279,531', issued iApril l Ofy the :relays of this selector, `only the switching, line, r'and 're-f f lease relays 92| to 623,one ofthe hunting relays' E24';^and. the :group '#9 relay'625 areshownx. The other'circuit apparatus and conductors `offthet `-selector are omitted,'as 4'the'detaifls ofthe selec-- tor form no part of this invention."

The connecting-link"circuit 'CLC"-`I of Fig."13' is' shown'in Fi'gsqljj'andf). This' connecting'-Y- link circuit is" accessible to the lselectors over the tip, ring, andisleeve conductors T, and 'S` ex`" tending toFigfl fromliig'-'Ggfand it`isinterconnected through cable CAQDR-l tothe distribuh tor DRM-I Fig. 6.

The connecting-link circuit CLC--I includes the illustrated control vrelays 'Hilltoll I of Fig. '7 the 'control relays 189| to' l8111 of Fig.-8; the tens",! unit'syrand party registers TR`,'UR, and PR of" -Fig'sLS and 9;andcontrol relay `9I?I 'ofFig'. 9.v

Along the 'lower portion of Figs. 8 and 9, and in Figs. 10 andvll, there is shown common'equlp-V mentwhichiisf-a portion of andfsupplemental to the yconimon'equipment of Figs. v1 to 3. The two portions of the common equipment are interconf nected by the tens and units rnarkingfcables l CLA-JIM and 'CA-' UM.

The-portion'of the common equipment shown`v` in. Figs. 8 @and `9 includes the marking terminal' blocksand B"-UM;` control relays 8 I0' and 9I0;and the tens, units`-, and party-identifying terminalblo'cks Bl-TI, B-i-UI, and B`-PI. Teinporary'jumpers may beattached tothe abovementionedfblocks Vfor markingand identifying purposes.'

The portion of the Vcommon equipment shown f in Figs; 10 'and 11 includescontrol relays lllto IIJ'IUf'I I`0I and VI I1!2, and the common-test equip; ment CT.` The Vcommon-test equipment vC'I "in'YV cludes control'rela'ysf I F03 tol I m9,? The common test equipment C'I is connected by cable CA--CT to all of the connecting-link circuits, such as- CLC-I of the same hundreds group.

DETAILED DESCRIPTION 5 v The; kdisclosure'l'iaving been described generally,L a detailed:zdescriptionzofzthe :operation .of Vthe )dise closed embodiment of the invention will now be given.

A call from substation A to substation B A description will rst be given of the operations involved when the subscriber at substation A calls the subscriber at substation B.

It is to be observed that the number of the line of substation A is 911, and that the number of the line of substation B is 916, the lines being both lines of the same large (1D0-line) group, and both of the same small (l-line) group. From the description which is to follow, it will be understood how any line of the system can call any other line thereof.

In order to cause a connection to be completed from the calling line 911 to the called line 916, the subscriber at substation A removes his receiver; waits for dial tone, which he hears when connection has been extended to a selector; and then dials the hundreds, tens, and units digits- 9, 1, and 6-in the desired number, followed by the nal digit 1 to cause ringing current to be applied to the called line.

Marking the calling 1li-line group and the calling line therein When the receiver (not shown) is removed at substation A, line relay 40| energizes over the calling line. Assuming that at least one of the primary switching devices IPA to IPD (Figs. 4 and 3) having access to the 10-line group in which the calling line is located is idle, the closure oi the inner contacts of line relay 40| places a starting battery potential on conductor ST' of the #l tens-groups cable CA-Gl over the following circuit; path: from battery, by way of the resistor 409, conductor 408, contacts of any unoperated one of the hold relays (such as 4I'|.and 421) of the associated primary group, conductor 401, conductor 406, common to all relays of the iirst -line group, inner contacts ofthe operated line relay 40|, to conductor 405.

At its lower contacts, line relay 40| places a marking ground potential on conductor I in cable CA-GI, The tens and units designation of the calling line is thus marked in cable CA-GL Assuming that the operation of line relay 40| occurs at an instant when all of the tens relays 2| I to 220 (and consequently relays 20| to 2|0) are in a restored condition, the previously described placing of a tens-marking battery potential on conductor ST of cable CA-GI results in the closure of an energizing circuit for group relays and 2|| in series, as follows: from battery potential on conductor ST of cable CA-G|, through the armature and back contact of group-cutoff relay 23|, winding of group relay 20|, the lower winding of group relay 2| I, normally closed contacts controlled by the lower armature of relay 2| I, common conductor 229, the inner lower contacts of all of the group relays 220 to 2| I in series, and thence to ground through contacts of clearout and transfer-control relays 222 and 22|. Group relays 20| and 2I| operate over this circuit.

Operating the units translator UT Upon operating, relay 20| connects the mark conductors to 0 of the group-1 cable CA-GI respectively with the conductors of units-mark cable CA--UM. The ground potential placed on the individual marking conductor I in the group-1 cable CA--GI by the lower contacts of line relay is thereby extended, through the uppermost contacts of relay 20 to conductor I of the unitsrnarking cable CA-UM, closing a circuit through the outermost contacts of relay 306, upper winding of relay 30|, inner upper contacts of relays 302 to 305, and thence to battery through the associated resistor. Relay 30| operates over this circuit. At its upper armature, it places a marking ground potential on conductor I or" the p-rimary marking cable CA-PM, while at its lower armature it connects conductor 6 in cable CA-UM to the marking relay 306, but relay 306 is not operated at this time, since the conductor S in cable CA-UM is grounded only when the sixth line in a tens group is calling or is being called, in which case relays 30| and 30E are both operated to ground both the rst and the sixth conductors in cable CA-PM.

At this point it should be noted that the relays 30| to 306 are so connected that the marking of only a single line can be impressed upon the conductors of cable CA-PM, even though two or more lines in the same 10-line group are calling simultaneously. For example, when relay 300 operates, which it does when any one of the sixth to tenth lines in a 10-line group is calling or is being called, it disconnects the conductors I to 5 of the cable CA-UM, associated respectively with the first to fifth lines of a group, whereby only the sixth Kto tenth conductors in cable CA-UM are effective to operate the relays 30| to 305 under that condition. The battery-chain contacts carried by relays 302 to 305 insure that no two of these relays can be operated at the same time. safeguard, the ground potential through which conductors 2 to 5 of the cable CA-PM can be marked is carried through chain contacts of relays 30| to 304.

The ground potential applied to conductor I of cable CA-PM is effective tc position whichever one of the primary switching devices IPA to IPD becomes connected up to extend the calling line.

Selecting the primary switching devices in the calling IU-Zine grOup Upon operating over its previously traced circuit, relay 2I at its lower armature, locks the lower terminal of its lower winding to ground through contacts of relays 222 and 22|, at the same time disconnecting its lower winding from the common conductor 229. At its inner armature, relay 2| I disconnects ground potential from conductor 220 to thereby prevent operation of any further group relays over a circuit such as that above traced. The removal of ground potential from conductor 229 also prevents operation of transfer-control relay 22| until the current nder action has been completed.

Relay 2|| also connects the conductors A to D of the primary-control cable CA-PC respectively to the conductors A to D of the first-group primary-control cable CA--PC|, therebyselecting the group of primary switching devices (|PA to IPD) having access to the 10-line group containing the calling line.

Matching an idle primary device with an idle finder-action secondary group An idle primary switching device in the calling primary group is now .to be matched with one of the secondary groups having an idle finder-action secondary device therein, responsive tothe described connecting up of the conducto-rs of the cable CA-PCI. It may be assumed that the relays |01 to IIO of the prefer- As an additional stored condition l at this time, -in Iwhich -Vevent secondary I group --A -has the Y-1: 1'eference, ZAfor groundI potential is extended (throught-contacts vof relays'V I I'and I) directlyI tothe inner ar- Vmature of the A relay-1030i the matching-cow trol group MC.

Let it be assumed now that allffourof t-hefprirnary switching devices" IPA to IPD,'Figs.4-iand A3, of the selected primaryngroup are lidleat I this` time. In this event, allV four 131- the-concerned hold relaysfsuch asillI'I anden?, are

restored, and =battery Apotential -is applied Vthrough; all four of the'connectingrelays-such Las 4-II)V and 42B, ,toall' lfour iof-y the-conductors -A to `D of the yassociated '.primaryecontrol'cable CA-,PCL Battery pmgential is thus extended,

through contacts of the operatedgroup relays '2II, and over the `four vconductors -or cable 4'CA-PC to the junction 'ofv the windings of Ithe respective relays 163 to-IBB of the-matching control group -MC. Letit be` assumed further that there yis at leastv one idle 1finder-action secondary jin-each of the four secondaryjgroups. iInthis event, 1 there is ground potential von the upper terminal of `the upper winding iof eachl-ef the relays IIiI toIE, asA will nowjoe pointed'out.

It isvto Ibe observed fthai-,the finder-actionsecondary vcable 'CA-FSleads from `equipment Y illustratedin 1 to the-four secondary-groups,

Acarrying-,l2 conductors, including group iicon- `ductorsl GA to Gllgassociatedl respectivelyywith theiinder-actionH secondary devices in secondary groups -A to AD. As gshownfiniig. 5, conductor GA inc able CA- -'FS, is commonY to f the-:finderaction ,secondaries'v in secondaryv 'group lgrandis suppliedV Wit-h ground potential rthrough contacts of the hold relay 501', aslong as the secondary device ISA is idle, and -is similarly supplied with ground potential at each' othereidleinder-action secondary device in group LA. Similarly, conduc- "tors GB to GDin vcable CA--FS-'extendlto the finder-action secondary devices in 4secondary -fgroupsB toD, respectively. vByf/this, arrange-ment,

under the presentgassumed conditions, each of the A,

conductor-s GA toGDof cab1eCA- FS,is grounded, wherebyisround potential. 'through contacts ,of the unoperateid relays l0. I and |112; is applied to the upperterminalof each ,of the relays VI 'SI3 y@alllfoilr y:lfltliese reIaysQperate, eachin series with the vconnecting relay (su'ch as td l0 .and T410) oftliecorrespondng v1ori1r1erv Ldevice IRA'. 'to'glPD None., of the: saidconnecting relays'however, can operate at this instant; because of ,the; indiol'ted vhigh resistance of the, upper windings, of relays IIl 3j to I 06.

With Epreference ground ,potential applied, as described, only to the armaturepf ltheijA relay y,through itslow-rresistanceV lower winding. E,ach of the relays I03.to' IZBB closes an operati ng.cir

. cuit for test-,cutoff relay 4U12, whereupon relay ',I'2 openecircuits theupper winding of eachrelay ID3 to |06, whereupon relaysfIM to-I,0,E im;me-'

diately restore. Relay |03, however, remains op- -ferated,- and relay :i4 HI operates; Yin the following locking circuit: from'g'roundfthrough contacts 0f the .unoperatedrelaysg I-I 'and' |918, lower ar- ;.mature and front .contact of relayI.0.3,-the vlowresistancelower- .winding'of relay m3,: conductor fA-.of cableCA--PC, contacts of1relay':2I.I,-con

'ductorA of cablefCA-PCI,fcontactsof kthe -un- 1 operated hold relay wlill, and the winding `of connectingvrelay M0, to battery.

"I'Firiding'4 thecallingilne The primary switching device IPA 1 is selected by the operation ofconnectin'g'relaydlfover its sistance lower winding off the lockedmatchingcontrol relayrIIlS. g'Relay dln-connectsthe-.conductors I toz `of theiprimaryfmarking cable CA-PM respectively f with the selective zrelays 4H toidl. Conductor Iof cableiGA-'PM has been;A marked by; ground: potential applied, theret to as previously described at the units trans- .latorUfI Fig.,;3, conductorsgzzto'fl,of this- ;cable beingunmarked. As ay result,;relay 4I Iy operates, but relays 4I2 to M6 remain unoperated.

l Upon operating.r relay 4 I I connects: tothe: tip, ring, and ,sleeve conductors'PT,-R,andes of :the Iztand iirglines in; thegassociated `IO-Iiriegroup, but the` connectingupxof the. #6; line ,is ,inelective; at this. time because'switching1relay Hilfre- Vmains unoperated, f,and onlythe-#I line of-the nected up. The tip, ring,f1and sleev e conductors of the calling line #9H v arethereby extended, through the uppermost set of contact pairs of relay IIII,andthence-through contacts of the unoperated switching relay4I6, to the tip, ring, and sleeve conductors of theprimary link PIA,

`extendingto the secondary multiple ,in the `A secondary group fMarking vthe actuated primary-switching f device The actuatedr primarygswitchng device IPA is marked in the FA secondaryrmultiplegto enable ,the linden-action:secondaryswitching `device. inV theA group which is. to operate toma-ke 'connec- -tiongwith the-actuatedlprimary zdevice IPA. This marking is 1zaccomplished only during the time :connecting relay; 4 i0 is Operated, being accom- Connecting, frelay M10, applies.l ground .potential vto 'the marking conductor M2 (not used bon any of the primaryswitchingdevicesV accessible n through selective positionszlgto 5of-ga secondary switch) Vand* it'papplies :a marking groundH poten- ,tial '.thloughpcontacts of -i hold relay4 lf1,rto1.the marking z-conductorfMI ,illustrated as 4'included in the primary link LP. I'A,ext ending1to the secondary multiple` ofthe :A-secondary-group.

Selecting a -nderfactionsecondary device in the .matched A group -As a further result of its above-described operation,` matching-control' relayl I-03 connects up conductor CA ofthe cable CA-FS, to prepare lfor the selection of a-finder-actondevice -inf the A secondary group.

At itslower armature, test-cutoi :relay `|132 closes a circuit, xthrough r`contactsof relay rlI I-Il, for=thefupper-lwinding of relay Hl!)l of the -pref- `erence group'-PG,'-Whereupon relay H19 `operates -a-nd applies lground lpotential `to uconductor I I I.

AWithrr'elays |04 to ldrestored, and relay |03 locked operated, the'grounding of conductor I II closes a circuit as follows: Vfrom ground, through the lower contacts of relay llilfcontacts of the operated relay LMV-.conductor `I LIV-contacts of the operated matching-control relay |03, contacts Nof the-unoperated 4transfer relayIULJcondu-ctor 'CA of cable CA-FS1ower contacts of the unop- Aerated 'hold :relay -1501 of secondaryfswltch ISA (assumingdevicegISA to be'idle),.and thence to `battery, through the winding of. connecting relay 22500. -fRelayfSIlIl thereuponoperatesr to Kselect de- 7 5 vice I SA for operation. 

